Many food products are packaged in modified atmosphere packaging, which generally includes a package in which the internal atmosphere of the product package comprises a modified gas in place of ambient air. Specifically, modified atmosphere packaging attempts to replace the oxygen-containing ambient air that would ordinarily be present in a food package, with another type of gas, for example carbon dioxide or nitrogen. An objective of packaging food products in reduced-oxygen packaging is to increase the shelf-life of the food products.
Known attempts for forming, filling and sealing modified atmosphere packages include processes in which the ambient air and much of the residual oxygen within the food product are extracted using a vacuum or similar technology or dispersed by saturation with a modified gas. A package can then be formed around the food product and a modified gas can be injected into the package prior to sealing to provide a food package with a modified internal atmosphere. Optionally, a vacuum may be applied to the sealed food package to remove the headspace therefrom. In known attempts, these processes are often performed in discrete, intermittent steps in a package forming apparatus into which the products are individually indexed and where the above steps are carried out in sequence with pauses between each step as the food products advance to the next step.
Specifically, in one such attempt, a bottom forming film is heated in a thermoforming machine to form a bottom pocket with sidewalls within a die. Vent holes are then formed on each side of the bottom pocket. A pin is inserted through the vent holes and disperses a modified atmosphere gas into the bottom pocket. A food product is indexed and deposited into the bottom pocket. The partially packaged food product is advanced into a vacuum chamber. A top film is aligned with and overlain upon the bottom pocket. Seals between the top film and the bottom pocket are formed by applying heat to locations of contact between the bottom pocket and the top film. This and other known approaches are intermittent and, thus, expend time required to advance from one step to the next. Moreover, this particular approach uses a relatively thick and expensive bottom sheet for thermoforming the lower pocket, such as compared to the top film. Additionally, if the size of the food product is changed, the die used for forming the bottom pocket often must be changed and sized to fit the new food product. This can require additional expense and downtime of the packaging equipment if the size of the food product being packaged is changed.